Conventionally, a liquid crystal display device provided with optical sensors has been known, as a device that realizes a touch sensor function and the like. In such a liquid crystal display device, from the viewpoint of the reduction of the number of components, and the like, optical sensors are formed monolithically in an active matrix substrate incorporated in a liquid crystal panel. A well-known example of such an optical sensor is a photodiode having a lateral structure.
In the photodiode having the lateral structure, if the intrinsic semiconductor region has a too large length in the direction parallel with the forward direction of the photodiode, a region in which photoexcitation occurs in response to received light does not extent over an entirety of the intrinsic semiconductor region. Consequently, the other region than the region where the photoexcitation occurs in response to received light functions as a resistive region, thereby causing a decrease in the output. On the other hand, if the intrinsic region has a too short length in the direction parallel with the forward direction of the photodiode, the region in which photoexcitation occurs in response to received light has a smaller area, thereby causing a decrease in the light conversion efficiency. Therefore, it is significantly important to make the intrinsic semiconductor region have a desirable length in the direction parallel with the forward direction of the photodiode, in the photodiode having the lateral structure. Further, it is significantly important also to suppress variations in the lengths of the intrinsic semiconductor regions in the direction parallel with the forward direction of the photodiode, in the photodiodes having the lateral structure.
Then, as described in WO 2008/133162 (Patent Document 1), it has been proposed to define the boundary between the p-type semiconductor region and the intrinsic semiconductor region, and the boundary between the n-type semiconductor region and the intrinsic semiconductor region with two metal lines provided above the silicon film.
It should be noted that in the photodiode described in Patent Document 1, appropriate voltages are applied to the two metal lines positioned above the intrinsic semiconductor regions, respectively, so that a region where photoexcitation occurs in response to received light should be concentrated to the center of the intrinsic semiconductor region. This causes the substantial length of the intrinsic semiconductor region in the direction parallel with the forward direction of the photodiode to be approximately the same as the distance between the two metal lines. Therefore, in order to set the substantial length of the intrinsic semiconductor region in the direction parallel with the forward direction of the photodiode to a desired length, it is necessary to consider the distance between the two metal lines.
However, in the case of the photodiode described in Patent Document 1, if the distance between the two metal lines is shortened simply, this causes the light receiving area to decrease, which leads to a problem of difficulty in obtaining sufficient detection sensitivity.